By race or ethnicity, a growing proportion of poor children are Hispanic, a record 37 percent of the total. Whites make up 30 percent, blacks 26 percent.
Nearly 2.2 million children were poor in California last year, the most of any state, but the child poverty rate was highest in Mississippi, where more than 1 in 3 children was poor. Nationwide, child poverty stood at 21.8 percent, unchanged from the previous year.
"Stubbornly high child poverty rates in the wake of the Great Recession suggest we have not yet turned the corner three years after its official end," said Marybeth Mattingly, director of research on vulnerable families at the University of New Hampshire's Carsey Institute.
The numbers also reflect widening economic inequality, an issue President Barack Obama has pledged would be a top priority of his administration to address. Upward mobility in the U.S. has been hurt by a tight job market and the longer-term disappearance of midskill jobs due to globalization and automation.
The new census data shows that lower-income households are a steadily increasing share of the population, while middle- to higher-income groups shrank or were flat.
In 2012, households earning less than $24,999 made up 24.4 percent of total households, up from 21.7 percent four years earlier. The share of households earning $50,000 to $99,999 slipped from 31.2 percent to 29.9 percent. Top-income households making more than $200,000 dipped less, from 5 percent to 4.6 percent over that period.
The still-weak economy also meant fewer household moves in 2012.
After showing signs of increased migration in 2011, fewer Americans were on the move, many because of few job opportunities or the inability to buy a home.
U.S. migration fell by 0.2 percent in 2012 after edging up the previous year. While the number of longer-distance moves remained steady at 2.3 percent, moves within a county edged lower to 9 percent, particularly among young adults 18-34.